This invention relates generally to filters and more particularly to methods and apparatus for tuning the bandwidth, or cut-off frequency, of such filters. Still more particularly, the invention relates to a method for minimizing cut-off frequency variation of such filters by using external reference components.
As is known in the art, an integrated circuit low pass filter using commonly available active and passive components will experience a large variation in the actual cut-off frequency due to the component dependencies on fabrication processes and temperature and can be controlled to a small variation (i.e., tolerance) in its value. Additionally, all stages in a multi-stage filter will vary independently. Such variations are undesirable in many applications.